The long-term goal of my project is to determine the role of reciprocal connections in cortical dynamics and "sensory perception". Here I shall investigate their effect on receptive field parameters and functional architecture of the primary visual cortex. Despite the fact that most cortical areas have descending or horizontal connections that are comparable to, or in some cases more massive than their corresponding ascending connections, the contribution of these reciprocal connections to the processing of visual information is almost completely unknown. During my time as a NRSA predoctorate recipient, I showed that reversible cryogenic inactivation of connections from the extrastriate region, area 18 (V2), alters both selectivity and functional structure of cat primary visual cortex (area 17 (V1)) (Sailstad et. al., 1999). However because cooling inactivated almost all the cortical layers, it is difficult to isolate and identify the neuronal circuitry through which area 18 produces changes in selectivity and functional architecture of area 17. Therefore to properly interpret this cooling data, I intend to use GABA injections instead of a cooling plate to inactivate a small region of a particular layer in cat area 18. While area 18 is inactivated, I will observe its effect on selectivity and function by simultaneously recording both the intrinsic optical signal and multi-unit extracellular signal from area 17. To determine the extent to which these connections contribute to dynamic receptive field properties, and to allow a valid interpretation of my results with regard to the role of reciprocal connections, I will inactivate area 18 and calculate its effect on dynamic orientation tuning with the reverse correlation method used by Ringach et. al. 1997.